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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 4526195eca5100f2a08601b9ac75d03230b9b9e2 / . / docs / WritingAnLLVMPass.html
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Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]6 <title>Writing an LLVM Pass</title>
7 <link rel="stylesheet" href="llvm.css" type="text/css">
8</head>
9<body>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]10
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]11<h1>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]12 Writing an LLVM Pass
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]13</h1>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]14
15<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]16 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]17 <li><a href="#quickstart">Quick Start - Writing hello world</a>
18 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]19 <li><a href="#makefile">Setting up the build environment</a></li>
20 <li><a href="#basiccode">Basic code required</a></li>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]21 <li><a href="#running">Running a pass with <tt>opt</tt></a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]22 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]23 <li><a href="#passtype">Pass classes and requirements</a>
24 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]25 <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]26 <li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]27 <ul>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]28 <li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]29 </ul></li>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]30 <li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
31 <ul>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]32 <li><a href="#doInitialization_scc">The <tt>doInitialization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]35 <li><a href="#doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]36 &amp;)</tt> method</a></li>
37 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]38 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
39 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]40 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]41 &amp;)</tt> method</a></li>
42 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]43 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]44 &amp;)</tt> method</a></li>
45 </ul></li>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]46 <li><a href="#LoopPass">The <tt>LoopPass</tt> class</a>
47 <ul>
48 <li><a href="#doInitialization_loop">The <tt>doInitialization(Loop *,
49 LPPassManager &amp;)</tt> method</a></li>
50 <li><a href="#runOnLoop">The <tt>runOnLoop</tt> method</a></li>
51 <li><a href="#doFinalization_loop">The <tt>doFinalization()
52 </tt> method</a></li>
53 </ul></li>
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]54 <li><a href="#RegionPass">The <tt>RegionPass</tt> class</a>
55 <ul>
56 <li><a href="#doInitialization_region">The <tt>doInitialization(Region *,
57 RGPassManager &amp;)</tt> method</a></li>
58 <li><a href="#runOnRegion">The <tt>runOnRegion</tt> method</a></li>
59 <li><a href="#doFinalization_region">The <tt>doFinalization()
60 </tt> method</a></li>
61 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]62 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
63 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]64 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]65 &amp;)</tt> method</a></li>
66 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
67 method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]68 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]69 &amp;)</tt> method</a></li>
70 </ul></li>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]71 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
72 class</a>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]73 <ul>
74 <li><a href="#runOnMachineFunction">The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]75 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
76 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]77 </ul>
78 <li><a href="#registration">Pass Registration</a>
79 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]80 <li><a href="#print">The <tt>print</tt> method</a></li>
81 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]82 <li><a href="#interaction">Specifying interactions between passes</a>
83 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]84 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
85 method</a></li>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]86 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
87 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a></li>
88 <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]89 <li><a href="#getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and
90<tt>getAnalysisIfAvailable&lt;&gt;</tt> methods</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]91 </ul></li>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]92 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
93 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]94 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
95 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
96 </ul></li>
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]97 <li><a href="#passStatistics">Pass Statistics</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]98 <li><a href="#passmanager">What PassManager does</a>
99 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]100 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
101 </ul></li>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]102 <li><a href="#registering">Registering dynamically loaded passes</a>
103 <ul>
104 <li><a href="#registering_existing">Using existing registries</a></li>
105 <li><a href="#registering_new">Creating new registries</a></li>
106 </ul></li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]107 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
108 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]109 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
110 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
111 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]112 <li><a href="#future">Future extensions planned</a>
113 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]114 <li><a href="#SMP">Multithreaded LLVM</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]115 </ul></li>
116</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000[diff] [blame]117
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]118<div class="doc_author">
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]119 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
Jim Laskeyc760a922007-03-14 19:32:21 +0000[diff] [blame]120 <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]121</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]122
123<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]124<h2>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]125 <a name="introduction">Introduction - What is a pass?</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]126</h2>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]127<!-- *********************************************************************** -->
128
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]129<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]130
131<p>The LLVM Pass Framework is an important part of the LLVM system, because LLVM
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]132passes are where most of the interesting parts of the compiler exist. Passes
133perform the transformations and optimizations that make up the compiler, they
134build the analysis results that are used by these transformations, and they are,
135above all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]136
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]137<p>All LLVM passes are subclasses of the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]138href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]139class, which implement functionality by overriding virtual methods inherited
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]140from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
141the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
142href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
143href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]144href="#LoopPass">LoopPass</a></tt>, or <tt><a
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]145href="#RegionPass">RegionPass</a></tt>, or <tt><a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]146href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
147more information about what your pass does, and how it can be combined with
148other passes. One of the main features of the LLVM Pass Framework is that it
149schedules passes to run in an efficient way based on the constraints that your
150pass meets (which are indicated by which class they derive from).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]151
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]152<p>We start by showing you how to construct a pass, everything from setting up
153the code, to compiling, loading, and executing it. After the basics are down,
154more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]155
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]156</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]157
158<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]159<h2>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]160 <a name="quickstart">Quick Start - Writing hello world</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]161</h2>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]162<!-- *********************************************************************** -->
163
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]164<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]165
166<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
167is designed to simply print out the name of non-external functions that exist in
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]168the program being compiled. It does not modify the program at all, it just
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]169inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]170source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]171
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]172<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]173<h3>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]174 <a name="makefile">Setting up the build environment</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]175</h3>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]176
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]177<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]178
Duncan Sandsdc97c0b2011-01-01 17:28:49 +0000[diff] [blame]179 <p>First, configure and build LLVM. This needs to be done directly inside the
180 LLVM source tree rather than in a separate objects directory.
181 Next, you need to create a new directory somewhere in the LLVM source
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]182 base. For this example, we'll assume that you made
Duncan Sandsdc97c0b2011-01-01 17:28:49 +0000[diff] [blame]183 <tt>lib/Transforms/Hello</tt>. Finally, you must set up a build script
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]184 (Makefile) that will compile the source code for the new pass. To do this,
185 copy the following into <tt>Makefile</tt>:</p>
NAKAMURA Takumi4d6deb02011-04-09 09:51:57 +0000[diff] [blame]186 <hr>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]187
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]188<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]189# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]190
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]191# Path to top level of LLVM hierarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]192LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]193
194# Name of the library to build
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]195LIBRARYNAME = Hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]196
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]197# Make the shared library become a loadable module so the tools can
198# dlopen/dlsym on the resulting library.
Robert Bocchino3cf817d2006-01-06 22:49:23 +0000[diff] [blame]199LOADABLE_MODULE = 1
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]200
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]201# Include the makefile implementation stuff
202include $(LEVEL)/Makefile.common
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]203</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]204
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]205<p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
Duncan Sands779ff7f2011-01-01 17:21:58 +0000[diff] [blame]206directory are to be compiled and linked together into a shared object
207<tt>$(LEVEL)/Debug+Asserts/lib/Hello.so</tt> that can be dynamically loaded by
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]208the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]209If your operating system uses a suffix other than .so (such as windows or
210Mac OS/X), the appropriate extension will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]211
Oscar Fuentes23ba1e42011-04-12 19:40:35 +0000[diff] [blame]212<p>If you are used CMake to build LLVM, see
213<a href="CMake.html#passdev">Developing an LLVM pass with CMake</a>.</p>
214
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]215<p>Now that we have the build scripts set up, we just need to write the code for
216the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]217
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]218</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]219
220<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]221<h3>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]222 <a name="basiccode">Basic code required</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]223</h3>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]224
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]225<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]226
227<p>Now that we have a way to compile our new pass, we just have to write it.
228Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]229
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]230<div class="doc_code">
231<pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]232<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
233<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]234<b>#include</b> "<a href="http://llvm.org/doxygen/raw__ostream_8h.html">llvm/Support/raw_ostream.h</a>"
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]235</pre>
236</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]237
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]238<p>Which are needed because we are writing a <tt><a
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]239href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>,
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]240we are operating on <tt><a
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]241href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s,
242and we will be doing some printing.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]243
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]244<p>Next we have:</p>
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]245
246<div class="doc_code">
247<pre>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]248<b>using namespace llvm;</b>
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]249</pre>
250</div>
251
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]252<p>... which is required because the functions from the include files
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]253live in the llvm namespace.</p>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]254
255<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]256
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]257<div class="doc_code">
258<pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]259<b>namespace</b> {
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]260</pre>
261</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]262
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]263<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]264what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]265things declared inside of the anonymous namespace visible only to the current
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]266file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]267information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]268
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]269<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]270
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]271<div class="doc_code">
272<pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]273 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]274</pre>
275</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]276
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]277<p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]278href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]279The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]280href="#passtype">later</a>, but for now, know that <a
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]281href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate on a function at a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]282time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]283
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]284<div class="doc_code">
285<pre>
286 static char ID;
Bill Wendlingb583e422011-12-09 19:11:02 +0000[diff] [blame]287 Hello() : FunctionPass(ID) {}
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]288</pre>
289</div>
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]290
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]291<p>This declares pass identifier used by LLVM to identify pass. This allows LLVM
292to avoid using expensive C++ runtime information.</p>
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]293
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]294<div class="doc_code">
295<pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]296 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]297 errs() &lt;&lt; "<i>Hello: </i>";
298 errs().write_escaped(F.getName()) &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]299 <b>return false</b>;
300 }
301 }; <i>// end of struct Hello</i>
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]302} <i>// end of anonymous namespace</i>
303</pre>
304</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]305
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]306<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
307which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]308href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
309to do our thing, so we just print out our message with the name of each
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]310function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]311
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]312<div class="doc_code">
313<pre>
314char Hello::ID = 0;
315</pre>
316</div>
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]317
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]318<p>We initialize pass ID here. LLVM uses ID's address to identify a pass, so
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]319initialization value is not important.</p>
320
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]321<div class="doc_code">
322<pre>
323static RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>",
324 false /* Only looks at CFG */,
325 false /* Analysis Pass */);
326</pre>
327</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]328
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]329<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
330giving it a command line argument "<tt>hello</tt>", and a name "<tt>Hello World
331Pass</tt>". The last two arguments describe its behavior: if a pass walks CFG
332without modifying it then the third argument is set to <tt>true</tt>; if a pass
333is an analysis pass, for example dominator tree pass, then <tt>true</tt> is
334supplied as the fourth argument.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]335
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]336<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]337
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]338<div class="doc_code">
339<pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]340<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
341<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]342<b>#include</b> "<a href="http://llvm.org/doxygen/raw__ostream_8h.html">llvm/Support/raw_ostream.h</a>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]343
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]344<b>using namespace llvm;</b>
345
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]346<b>namespace</b> {
347 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]348
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]349 static char ID;
Bill Wendlingb583e422011-12-09 19:11:02 +0000[diff] [blame]350 Hello() : FunctionPass(ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]351
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]352 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]353 errs() &lt;&lt; "<i>Hello: </i>";
354 errs().write_escaped(F.getName()) &lt;&lt; '\n';
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]355 <b>return false</b>;
356 }
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]357
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]358 };
359}
360
361char Hello::ID = 0;
362static RegisterPass&lt;Hello&gt; X("hello", "Hello World Pass", false, false);
363</pre>
364</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]365
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]366<p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
Duncan Sands779ff7f2011-01-01 17:21:58 +0000[diff] [blame]367command in the local directory and you should get a new file
368"<tt>Debug+Asserts/lib/Hello.so</tt>" under the top level directory of the LLVM
369source tree (not in the local directory). Note that everything in this file is
Bill Wendlingb99d5b02011-10-11 07:03:52 +0000[diff] [blame]370contained in an anonymous namespace &mdash; this reflects the fact that passes
371are self contained units that do not need external interfaces (although they can
372have them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]373
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]374</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]375
376<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]377<h3>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]378 <a name="running">Running a pass with <tt>opt</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]379</h3>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]380
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]381<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]382
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]383<p>Now that you have a brand new shiny shared object file, we can use the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]384<tt>opt</tt> command to run an LLVM program through your pass. Because you
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]385registered your pass with <tt>RegisterPass</tt>, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]386use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]387
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]388<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]389href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]390LLVM. We can now run the bitcode file (<tt>hello.bc</tt>) for the program
391through our transformation like this (or course, any bitcode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]392work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]393
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]394<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]395$ opt -load ../../../Debug+Asserts/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]396Hello: __main
397Hello: puts
398Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]399</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]400
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]401<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
402pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
403argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]404pass</a>). Because the hello pass does not modify the program in any
405interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]406<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]407
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]408<p>To see what happened to the other string you registered, try running
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]409<tt>opt</tt> with the <tt>-help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]410
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]411<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]412$ opt -load ../../../Debug+Asserts/lib/Hello.so -help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]413OVERVIEW: llvm .bc -&gt; .bc modular optimizer
414
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]415USAGE: opt [options] &lt;input bitcode&gt;
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]416
417OPTIONS:
418 Optimizations available:
419...
420 -funcresolve - Resolve Functions
421 -gcse - Global Common Subexpression Elimination
422 -globaldce - Dead Global Elimination
423 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]424 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]425 -inline - Function Integration/Inlining
426 -instcombine - Combine redundant instructions
427...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]428</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]429
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]430<p>The pass name get added as the information string for your pass, giving some
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]431documentation to users of <tt>opt</tt>. Now that you have a working pass, you
432would go ahead and make it do the cool transformations you want. Once you get
433it all working and tested, it may become useful to find out how fast your pass
434is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
435line option (<tt>--time-passes</tt>) that allows you to get information about
436the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]437example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]438
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]439<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]440$ opt -load ../../../Debug+Asserts/lib/Hello.so -hello -time-passes &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]441Hello: __main
442Hello: puts
443Hello: main
444===============================================================================
445 ... Pass execution timing report ...
446===============================================================================
447 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
448
449 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]450 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]451 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
452 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
453 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
454 0.0100 (100.0%) 0.0100 (100.0%) 0.0200 (100.0%) 0.0479 (100.0%) TOTAL
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]455</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]456
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]457<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]458passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
459that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]460hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]461
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]462<p>Now that you have seen the basics of the mechanics behind passes, we can talk
463about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]464
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]465</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]466
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]467</div>
468
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]469<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]470<h2>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]471 <a name="passtype">Pass classes and requirements</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]472</h2>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]473<!-- *********************************************************************** -->
474
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]475<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]476
477<p>One of the first things that you should do when designing a new pass is to
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]478decide what class you should subclass for your pass. The <a
479href="#basiccode">Hello World</a> example uses the <tt><a
480href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
481did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]482available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]483
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]484<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]485specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]486listed. This gives the LLVM Pass Infrastructure information necessary to
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]487optimize how passes are run, so that the resultant compiler isn't unnecessarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]488slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]489
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]490<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]491<h3>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]492 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]493</h3>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]494
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]495<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]496
497<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]498href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]499class. This pass type is used for passes that do not have to be run, do not
500change state, and never need to be updated. This is not a normal type of
501transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]502compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]503
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]504<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]505providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]506other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]507
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]508<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
509invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]510
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]511</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]512
513<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]514<h3>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]515 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]516</h3>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]517
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]518<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]519
520<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]521href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]522class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]523<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]524referring to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]525functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Daniel Dunbarb71725b2009-07-01 23:38:44 +0000[diff] [blame]526subclasses, no optimization can be done for their execution.</p>
527
528<p>A module pass can use function level passes (e.g. dominators) using
529the getAnalysis interface
530<tt>getAnalysis&lt;DominatorTree&gt;(llvm::Function *)</tt> to provide the
531function to retrieve analysis result for, if the function pass does not require
Devang Patel468857f2009-08-10 16:37:29 +0000[diff] [blame]532any module or immutable passes. Note that this can only be done for functions for which the
Daniel Dunbarb71725b2009-07-01 23:38:44 +0000[diff] [blame]533analysis ran, e.g. in the case of dominators you should only ask for the
534DominatorTree for function definitions, not declarations.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]535
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]536<p>To write a correct <tt>ModulePass</tt> subclass, derive from
537<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
538following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]539
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]540<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]541<h4>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]542 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]543</h4>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]544
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]545<div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]546
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]547<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]548 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]549</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]550
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]551<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
552It should return true if the module was modified by the transformation and
553false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]554
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]555</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]556
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]557</div>
558
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]559<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]560<h3>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]561 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]562</h3>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]563
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]564<div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]565
566<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]567href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]568is used by passes that need to traverse the program bottom-up on the call graph
569(callees before callers). Deriving from CallGraphSCCPass provides some
570mechanics for building and traversing the CallGraph, but also allows the system
571to optimize execution of CallGraphSCCPass's. If your pass meets the
572requirements outlined below, and doesn't meet the requirements of a <tt><a
573href="#FunctionPass">FunctionPass</a></tt> or <tt><a
574href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
575<tt>CallGraphSCCPass</tt>.</p>
576
577<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
578
579<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
580
581<ol>
582
Nick Lewycky99597062011-01-03 06:16:07 +0000[diff] [blame]583<li>... <em>not allowed</em> to inspect or modify any <tt>Function</tt>s other
584than those in the current SCC and the direct callers and direct callees of the
585SCC.</li>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]586
587<li>... <em>required</em> to preserve the current CallGraph object, updating it
588to reflect any changes made to the program.</li>
589
590<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
591though they may change the contents of an SCC.</li>
592
593<li>... <em>allowed</em> to add or remove global variables from the current
594Module.</li>
595
596<li>... <em>allowed</em> to maintain state across invocations of
597 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
598</ol>
599
600<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
601because it has to handle SCCs with more than one node in it. All of the virtual
602methods described below should return true if they modified the program, or
603false if they didn't.</p>
604
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]605<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]606<h4>
607 <a name="doInitialization_scc">
608 The <tt>doInitialization(CallGraph &amp;)</tt> method
609 </a>
610</h4>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]611
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]612<div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]613
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]614<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]615 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]616</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]617
618<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
619<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
620functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
621is designed to do simple initialization type of stuff that does not depend on
622the SCCs being processed. The <tt>doInitialization</tt> method call is not
623scheduled to overlap with any other pass executions (thus it should be very
624fast).</p>
625
626</div>
627
628<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]629<h4>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]630 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]631</h4>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]632
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]633<div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]634
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]635<div class="doc_code"><pre>
Chris Lattner6f25d9f2010-04-16 23:07:44 +0000[diff] [blame]636 <b>virtual bool</b> runOnSCC(CallGraphSCC &amp;SCC) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]637</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]638
639<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
640should return true if the module was modified by the transformation, false
641otherwise.</p>
642
643</div>
644
645<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]646<h4>
647 <a name="doFinalization_scc">
648 The <tt>doFinalization(CallGraph &amp;)</tt> method
649 </a>
650</h4>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]651
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]652<div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]653
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]654<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]655 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]656</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]657
658<p>The <tt>doFinalization</tt> method is an infrequently used method that is
659called when the pass framework has finished calling <a
660href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
661program being compiled.</p>
662
663</div>
664
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]665</div>
666
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]667<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]668<h3>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]669 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]670</h3>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]671
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]672<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]673
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]674<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]675href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]676subclasses do have a predictable, local behavior that can be expected by the
677system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]678independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]679<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]680order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]681
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]682<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]683
684<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]685<li>Modify a Function other than the one currently being processed.</li>
686<li>Add or remove Function's from the current Module.</li>
687<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]688<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]689 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
690</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]691
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]692<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]693href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
694may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]695should return true if they modified the program, or false if they didn't.</p>
696
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]697<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]698<h4>
699 <a name="doInitialization_mod">
700 The <tt>doInitialization(Module &amp;)</tt> method
701 </a>
702</h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]703
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]704<div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]705
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]706<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]707 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]708</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]709
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]710<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]711<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]712functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
713is designed to do simple initialization type of stuff that does not depend on
714the functions being processed. The <tt>doInitialization</tt> method call is not
715scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]716fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]717
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]718<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]719href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]720pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]721platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]722uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]723free functions that it needs, adding prototypes to the module if necessary.</p>
724
725</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]726
727<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]728<h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]729 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]730</h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]731
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]732<div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]733
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]734<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]735 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]736</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]737
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]738<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
739the transformation or analysis work of your pass. As usual, a true value should
740be returned if the function is modified.</p>
741
742</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]743
744<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]745<h4>
746 <a name="doFinalization_mod">
747 The <tt>doFinalization(Module &amp;)</tt> method
748 </a>
749</h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]750
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]751<div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]752
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]753<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]754 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]755</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]756
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]757<p>The <tt>doFinalization</tt> method is an infrequently used method that is
758called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]759href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]760program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]761
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]762</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]763
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]764</div>
765
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]766<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]767<h3>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]768 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]769</h3>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]770
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]771<div>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]772
773<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
774all of the other loops in the function. <tt>LoopPass</tt> processes loops in
775loop nest order such that outer most loop is processed last. </p>
776
777<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
778<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
Jay Foad71001c92011-04-07 12:41:09 +0000[diff] [blame]779straightforward. <tt>LoopPass</tt>'s may overload three virtual methods to
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]780do their work. All these methods should return true if they modified the
781program, or false if they didn't. </p>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]782
783<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]784<h4>
785 <a name="doInitialization_loop">
786 The <tt>doInitialization(Loop *,LPPassManager &amp;)</tt> method
787 </a>
788</h4>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]789
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]790<div>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]791
792<div class="doc_code"><pre>
793 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
794</pre></div>
795
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]796<p>The <tt>doInitialization</tt> method is designed to do simple initialization
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]797type of stuff that does not depend on the functions being processed. The
798<tt>doInitialization</tt> method call is not scheduled to overlap with any
799other pass executions (thus it should be very fast). LPPassManager
800interface should be used to access Function or Module level analysis
801information.</p>
802
803</div>
804
805
806<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]807<h4>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]808 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]809</h4>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]810
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]811<div>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]812
813<div class="doc_code"><pre>
814 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
815</pre></div><p>
816
817<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
818the transformation or analysis work of your pass. As usual, a true value should
819be returned if the function is modified. <tt>LPPassManager</tt> interface
820should be used to update loop nest.</p>
821
822</div>
823
824<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]825<h4>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]826 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]827</h4>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]828
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]829<div>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]830
831<div class="doc_code"><pre>
832 <b>virtual bool</b> doFinalization();
833</pre></div>
834
835<p>The <tt>doFinalization</tt> method is an infrequently used method that is
836called when the pass framework has finished calling <a
837href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
838program being compiled. </p>
839
840</div>
841
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]842</div>
843
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]844<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]845<h3>
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]846 <a name="RegionPass">The <tt>RegionPass</tt> class </a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]847</h3>
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]848
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]849<div>
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]850
851<p> <tt>RegionPass</tt> is similar to <a href="#LoopPass"><tt>LoopPass</tt></a>,
852but executes on each single entry single exit region in the function.
853<tt>RegionPass</tt> processes regions in nested order such that the outer most
854region is processed last. </p>
855
856<p> <tt>RegionPass</tt> subclasses are allowed to update the region tree by using
857the <tt>RGPassManager</tt> interface. You may overload three virtual methods of
Jay Foad71001c92011-04-07 12:41:09 +0000[diff] [blame]858<tt>RegionPass</tt> to implement your own region pass. All these
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]859methods should return true if they modified the program, or false if they didn not.
860</p>
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]861
862<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]863<h4>
864 <a name="doInitialization_region">
865 The <tt>doInitialization(Region *, RGPassManager &amp;)</tt> method
866 </a>
867</h4>
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]868
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]869<div>
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]870
871<div class="doc_code"><pre>
872 <b>virtual bool</b> doInitialization(Region *, RGPassManager &amp;RGM);
873</pre></div>
874
875<p>The <tt>doInitialization</tt> method is designed to do simple initialization
876type of stuff that does not depend on the functions being processed. The
877<tt>doInitialization</tt> method call is not scheduled to overlap with any
878other pass executions (thus it should be very fast). RPPassManager
879interface should be used to access Function or Module level analysis
880information.</p>
881
882</div>
883
884
885<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]886<h4>
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]887 <a name="runOnRegion">The <tt>runOnRegion</tt> method</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]888</h4>
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]889
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]890<div>
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]891
892<div class="doc_code"><pre>
893 <b>virtual bool</b> runOnRegion(Region *, RGPassManager &amp;RGM) = 0;
894</pre></div><p>
895
896<p>The <tt>runOnRegion</tt> method must be implemented by your subclass to do
897the transformation or analysis work of your pass. As usual, a true value should
898be returned if the region is modified. <tt>RGPassManager</tt> interface
899should be used to update region tree.</p>
900
901</div>
902
903<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]904<h4>
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]905 <a name="doFinalization_region">The <tt>doFinalization()</tt> method</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]906</h4>
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]907
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]908<div>
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]909
910<div class="doc_code"><pre>
911 <b>virtual bool</b> doFinalization();
912</pre></div>
913
914<p>The <tt>doFinalization</tt> method is an infrequently used method that is
915called when the pass framework has finished calling <a
916href="#runOnRegion"><tt>runOnRegion</tt></a> for every region in the
917program being compiled. </p>
918
919</div>
920
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]921</div>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]922
923<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]924<h3>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]925 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]926</h3>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]927
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]928<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]929
930<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]931href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
932their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]933As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]934
935<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]936<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]937<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]938 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]939<li>Modify the control flow graph (by altering terminator instructions)</li>
940<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]941 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
942</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]943
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]944<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]945optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]946href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
947href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]948href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
949
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]950<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]951<h4>
952 <a name="doInitialization_fn">
953 The <tt>doInitialization(Function &amp;)</tt> method
954 </a>
955</h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]956
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]957<div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]958
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]959<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]960 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]961</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]962
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]963<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]964<tt>BasicBlockPass</tt>'s are not allowed to do, but that
965<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]966to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]967BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
968scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]969fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]970
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]971</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]972
973<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]974<h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]975 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]976</h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]977
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]978<div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]979
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]980<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]981 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]982</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]983
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]984<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]985function is not allowed to inspect or modify basic blocks other than the
986parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]987if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]988
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]989</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]990
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]991<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]992<h4>
993 <a name="doFinalization_fn">
994 The <tt>doFinalization(Function &amp;)</tt> method
995 </a>
996</h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]997
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]998<div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]999
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1000<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]1001 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1002</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]1003
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1004<p>The <tt>doFinalization</tt> method is an infrequently used method that is
1005called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]1006href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
1007program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1008finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]1009
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1010</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]1011
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1012</div>
1013
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]1014<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1015<h3>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1016 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1017</h3>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]1018
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1019<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1020
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1021<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
1022executes on the machine-dependent representation of each LLVM function in the
Dan Gohman9f116aa2010-03-10 01:29:39 +0000[diff] [blame]1023program.</p>
1024
1025<p>Code generator passes are registered and initialized specially by
1026<tt>TargetMachine::addPassesToEmitFile</tt> and similar routines, so they
1027cannot generally be run from the <tt>opt</tt> or <tt>bugpoint</tt>
1028commands.</p>
1029
1030<p>A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]1031the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1032<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
1033<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]1034
1035<ol>
Dan Gohman9f116aa2010-03-10 01:29:39 +0000[diff] [blame]1036<li>Modify or create any LLVM IR Instructions, BasicBlocks, Arguments,
1037 Functions, GlobalVariables, GlobalAliases, or Modules.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1038<li>Modify a MachineFunction other than the one currently being processed.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1039<li>Maintain state across invocations of <a
1040href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
1041data)</li>
1042</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]1043
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1044<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1045<h4>
1046 <a name="runOnMachineFunction">
1047 The <tt>runOnMachineFunction(MachineFunction &amp;MF)</tt> method
1048 </a>
1049</h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1050
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1051<div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1052
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1053<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1054 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1055</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1056
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1057<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
1058<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
1059work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1060
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1061<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1062<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1063<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
1064representation of the function. If you want to get at the LLVM <tt>Function</tt>
1065for the <tt>MachineFunction</tt> you're working on, use
1066<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
1067remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
1068<tt>MachineFunctionPass</tt>.</p>
1069
1070</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1071
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1072</div>
1073
1074</div>
1075
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1076<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1077<h2>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1078 <a name="registration">Pass registration</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1079</h2>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1080<!-- *********************************************************************** -->
1081
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1082<div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1083
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1084<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
1085pass registration works, and discussed some of the reasons that it is used and
1086what it does. Here we discuss how and why passes are registered.</p>
1087
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]1088<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
1089template. The template parameter is the name of the pass that is to be used on
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1090the command line to specify that the pass should be added to a program (for
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]1091example, with <tt>opt</tt> or <tt>bugpoint</tt>). The first argument is the
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1092name of the pass, which is to be used for the <tt>-help</tt> output of
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1093programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1094well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1095
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1096<p>If you want your pass to be easily dumpable, you should
1097implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1098
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1099<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1100<h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1101 <a name="print">The <tt>print</tt> method</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1102</h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1103
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1104<div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1105
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1106<div class="doc_code"><pre>
Torok Edwin52790e52008-10-28 17:29:23 +0000[diff] [blame]1107 <b>virtual void</b> print(std::ostream &amp;O, <b>const</b> Module *M) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1108</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1109
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1110<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
1111a human readable version of the analysis results. This is useful for debugging
1112an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1113works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1114
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1115<p>The <tt>llvm::OStream</tt> parameter specifies the stream to write the results on,
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1116and the <tt>Module</tt> parameter gives a pointer to the top level module of the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1117program that has been analyzed. Note however that this pointer may be null in
1118certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
1119debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1120depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1121
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1122</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1123
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1124</div>
1125
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1126<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1127<h2>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1128 <a name="interaction">Specifying interactions between passes</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1129</h2>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1130<!-- *********************************************************************** -->
1131
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1132<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1133
John Criswell8528e782007-12-03 19:34:25 +0000[diff] [blame]1134<p>One of the main responsibilities of the <tt>PassManager</tt> is to make sure
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1135that passes interact with each other correctly. Because <tt>PassManager</tt>
1136tries to <a href="#passmanager">optimize the execution of passes</a> it must
1137know how the passes interact with each other and what dependencies exist between
1138the various passes. To track this, each pass can declare the set of passes that
1139are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1140invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1141
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1142<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1143computed before your pass is run. Running arbitrary transformation passes can
1144invalidate the computed analysis results, which is what the invalidation set
1145specifies. If a pass does not implement the <tt><a
1146href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1147having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1148
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1149<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1150<h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1151 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1152</h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1153
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1154<div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1155
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1156<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1157 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1158</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1159
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1160<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1161invalidated sets may be specified for your transformation. The implementation
1162should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1163href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1164object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1165do this, a pass may call any of the following methods on the AnalysisUsage
1166object:</p>
1167</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1168
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1169<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1170<h4>
1171 <a name="AU::addRequired">
1172 The <tt>AnalysisUsage::addRequired&lt;&gt;</tt>
1173 and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods
1174 </a>
1175</h4>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1176
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1177<div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1178<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1179If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1180it can use one of these methods to arrange for it to be run before your pass.
1181LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1182spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1183Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1184be no critical edges in the CFG when your pass has been run.
1185</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1186
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1187<p>
1188Some analyses chain to other analyses to do their job. For example, an <a
1189href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1190href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1191cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1192used instead of the <tt>addRequired</tt> method. This informs the PassManager
1193that the transitively required pass should be alive as long as the requiring
1194pass is.
1195</p>
1196</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1197
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1198<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1199<h4>
1200 <a name="AU::addPreserved">
1201 The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method
1202 </a>
1203</h4>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1204
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1205<div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1206<p>
1207One of the jobs of the PassManager is to optimize how and when analyses are run.
1208In particular, it attempts to avoid recomputing data unless it needs to. For
1209this reason, passes are allowed to declare that they preserve (i.e., they don't
1210invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1211constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1212results of dominator analysis. By default, all passes are assumed to invalidate
1213all others.
1214</p>
1215
1216<p>
1217The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1218certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1219the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1220not modify the LLVM program at all (which is true for analyses), and the
1221<tt>setPreservesCFG</tt> method can be used by transformations that change
1222instructions in the program but do not modify the CFG or terminator instructions
1223(note that this property is implicitly set for <a
1224href="#BasicBlockPass">BasicBlockPass</a>'s).
1225</p>
1226
1227<p>
1228<tt>addPreserved</tt> is particularly useful for transformations like
1229<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1230and dominator related analyses if they exist, so it can preserve them, despite
1231the fact that it hacks on the CFG.
1232</p>
1233</div>
1234
1235<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1236<h4>
1237 <a name="AU::examples">
1238 Example implementations of <tt>getAnalysisUsage</tt>
1239 </a>
1240</h4>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1241
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1242<div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1243
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1244<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1245 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1246 <b>void</b> <a href="http://llvm.org/doxygen/structLICM.html">LICM</a>::getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
Chris Lattner8291e042002-10-21 19:57:59 +0000[diff] [blame]1247 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1248 AU.addRequired&lt;<a href="http://llvm.org/doxygen/classllvm_1_1LoopInfo.html">LoopInfo</a>&gt;();
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1249 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1250</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1251
1252</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1253
1254<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1255<h4>
1256 <a name="getAnalysis">
1257 The <tt>getAnalysis&lt;&gt;</tt> and
1258 <tt>getAnalysisIfAvailable&lt;&gt;</tt> methods
1259 </a>
1260</h4>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1261
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1262<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1263
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1264<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1265your class, providing you with access to the passes that you declared that you
1266required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1267method. It takes a single template argument that specifies which pass class you
1268want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1269
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1270<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1271 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1272 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1273 ...
1274 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1275</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1276
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1277<p>This method call returns a reference to the pass desired. You may get a
1278runtime assertion failure if you attempt to get an analysis that you did not
1279declare as required in your <a
1280href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1281method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1282other local method invoked by your <tt>run*</tt> method.
1283
1284A module level pass can use function level analysis info using this interface.
1285For example:</p>
1286
1287<div class="doc_code"><pre>
1288 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1289 ...
Devang Patelf23de112007-04-17 00:17:11 +0000[diff] [blame]1290 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1291 ...
1292 }
1293</pre></div>
1294
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1295<p>In above example, runOnFunction for DominatorTree is called by pass manager
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1296before returning a reference to the desired pass.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1297
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1298<p>
1299If your pass is capable of updating analyses if they exist (e.g.,
1300<tt>BreakCriticalEdges</tt>, as described above), you can use the
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1301<tt>getAnalysisIfAvailable</tt> method, which returns a pointer to the analysis
1302if it is active. For example:</p>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1303
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1304<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1305 ...
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1306 if (DominatorSet *DS = getAnalysisIfAvailable&lt;DominatorSet&gt;()) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1307 <i>// A DominatorSet is active. This code will update it.</i>
1308 }
1309 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1310</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1311
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1312</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1313
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1314</div>
1315
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1316<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1317<h2>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1318 <a name="analysisgroup">Implementing Analysis Groups</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1319</h2>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1320<!-- *********************************************************************** -->
1321
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1322<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1323
Chris Lattnerb7632282007-11-16 05:32:05 +0000[diff] [blame]1324<p>Now that we understand the basics of how passes are defined, how they are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1325used, and how they are required from other passes, it's time to get a little bit
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1326fancier. All of the pass relationships that we have seen so far are very
1327simple: one pass depends on one other specific pass to be run before it can run.
1328For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1329required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1330
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1331<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1332interface to the analysis results, but multiple ways of calculating them.
1333Consider alias analysis for example. The most trivial alias analysis returns
1334"may alias" for any alias query. The most sophisticated analysis a
1335flow-sensitive, context-sensitive interprocedural analysis that can take a
1336significant amount of time to execute (and obviously, there is a lot of room
1337between these two extremes for other implementations). To cleanly support
1338situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1339Analysis Groups.</p>
1340
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1341<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1342<h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1343 <a name="agconcepts">Analysis Group Concepts</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1344</h4>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1345
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1346<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1347
1348<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1349multiple different passes. Analysis Groups can be given human readable names
1350just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1351class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1352the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1353
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1354<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1355<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1356In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1357scans the available passes to see if any implementations of the analysis group
1358are available. If none is available, the default implementation is created for
1359the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1360between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1361
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1362<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1363passes, all analysis group implementations must be registered, and must use the
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1364<A href="#registerag"><tt>INITIALIZE_AG_PASS</tt></a> template to join the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1365implementation pool. Also, a default implementation of the interface
1366<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1367href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1368
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1369<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1370href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1371analysis group. The default implementation of the alias analysis interface (the
1372<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1373href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1374pass) just does a few simple checks that don't require significant analysis to
1375compute (such as: two different globals can never alias each other, etc).
1376Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1377href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1378interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1379href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1380not care which implementation of alias analysis is actually provided, they just
1381use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1382
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1383<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1384command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1385instantiated and added to the pass sequence. Issuing the command '<tt>opt
1386-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1387<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1388hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1389
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1390</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1391
1392<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1393<h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1394 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1395</h4>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1396
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1397<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1398
1399<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1400group itself, while the <tt>INITIALIZE_AG_PASS</tt> is used to add pass
1401implementations to the analysis group. First,
1402an analysis group should be registered, with a human readable name
1403provided for it.
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1404Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1405for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1406
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1407<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1408 <b>static</b> RegisterAnalysisGroup&lt;<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>&gt; A("<i>Alias Analysis</i>");
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1409</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1410
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1411<p>Once the analysis is registered, passes can declare that they are valid
1412implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1413
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1414<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1415<b>namespace</b> {
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1416 //<i> Declare that we implement the AliasAnalysis interface</i>
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1417 INITIALIZE_AG_PASS(FancyAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>somefancyaa</i>",
1418 "<i>A more complex alias analysis implementation</i>",
1419 false, // <i>Is CFG Only?</i>
1420 true, // <i>Is Analysis?</i>
1421 false, // <i>Is default Analysis Group implementation?</i>
1422 );
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1423}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1424</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1425
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1426<p>This just shows a class <tt>FancyAA</tt> that
1427uses the <tt>INITIALIZE_AG_PASS</tt> macro both to register and
1428to "join" the <tt><a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1429analysis group. Every implementation of an analysis group should join using
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1430this macro.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1431
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1432<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1433<b>namespace</b> {
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1434 //<i> Declare that we implement the AliasAnalysis interface</i>
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1435 INITIALIZE_AG_PASS(BasicAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>basicaa</i>",
1436 "<i>Basic Alias Analysis (default AA impl)</i>",
1437 false, // <i>Is CFG Only?</i>
1438 true, // <i>Is Analysis?</i>
1439 true, // <i>Is default Analysis Group implementation?</i>
1440 );
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1441}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1442</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1443
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1444<p>Here we show how the default implementation is specified (using the final
1445argument to the <tt>INITIALIZE_AG_PASS</tt> template). There must be exactly
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1446one default implementation available at all times for an Analysis Group to be
Devang Patel2397f8d2007-06-20 18:51:14 +0000[diff] [blame]1447used. Only default implementation can derive from <tt>ImmutablePass</tt>.
1448Here we declare that the
1449 <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1450pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1451
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1452</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1453
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1454</div>
1455
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1456<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1457<h2>
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1458 <a name="passStatistics">Pass Statistics</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1459</h2>
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1460<!-- *********************************************************************** -->
1461
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1462<div>
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1463<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1464href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1465class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1466metrics from passes. These statistics are printed at the end of a
1467run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1468line. See the <a href="http://llvm.org/docs/ProgrammersManual.html#Statistic">Statistics section</a> in the Programmer's Manual for details.
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1469
1470</div>
1471
1472
1473<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1474<h2>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1475 <a name="passmanager">What PassManager does</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1476</h2>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1477<!-- *********************************************************************** -->
1478
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1479<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1480
1481<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1482href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1483<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1484href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1485takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1486are set up correctly, and then schedules passes to run efficiently. All of the
1487LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1488passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1489
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1490<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1491time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1492
1493<ol>
1494<li><b>Share analysis results</b> - The PassManager attempts to avoid
1495recomputing analysis results as much as possible. This means keeping track of
1496which analyses are available already, which analyses get invalidated, and which
1497analyses are needed to be run for a pass. An important part of work is that the
1498<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1499it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1500results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1501
1502<li><b>Pipeline the execution of passes on the program</b> - The
1503<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1504of a series of passes by pipelining the passes together. This means that, given
Duncan Sandsab4c3662011-02-15 09:23:02 +0000[diff] [blame]1505a series of consecutive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1506will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1507the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1508href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1509etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1510
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1511<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1512the LLVM program representation for a single function at a time, instead of
1513traversing the entire program. It reduces the memory consumption of compiler,
1514because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1515href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
John Criswell9795bb82007-12-10 20:26:29 +0000[diff] [blame]1516needs to be calculated at a time. This also makes it possible to implement
1517some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1518href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1519
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1520</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1521
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1522<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1523much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1524example, the "preserved" set is intentionally conservative in the face of an
1525unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1526Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1527allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1528
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1529<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1530options that is useful for debugging pass execution, seeing how things work, and
1531diagnosing when you should be preserving more analyses than you currently are
1532(To get information about all of the variants of the <tt>--debug-pass</tt>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1533option, just type '<tt>opt -help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1534
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1535<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1536how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1537Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1538
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1539<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1540$ opt -load ../../../Debug+Asserts/lib/Hello.so -gcse -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1541Module Pass Manager
1542 Function Pass Manager
1543 Dominator Set Construction
1544 Immediate Dominators Construction
1545 Global Common Subexpression Elimination
1546-- Immediate Dominators Construction
1547-- Global Common Subexpression Elimination
1548 Natural Loop Construction
1549 Loop Invariant Code Motion
1550-- Natural Loop Construction
1551-- Loop Invariant Code Motion
1552 Module Verifier
1553-- Dominator Set Construction
1554-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1555 Bitcode Writer
1556--Bitcode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1557</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1558
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1559<p>This output shows us when passes are constructed and when the analysis
1560results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1561GCSE uses dominator and immediate dominator information to do its job. The LICM
1562pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1563dominators. Because immediate dominators are no longer useful after the GCSE
1564pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1565compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1566
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1567<p>After the LICM pass, the module verifier runs (which is automatically added
1568by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1569resultant LLVM code is well formed. After it finishes, the dominator set
1570information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1571passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1572
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1573<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1574World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1575
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1576<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1577$ opt -load ../../../Debug+Asserts/lib/Hello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1578Module Pass Manager
1579 Function Pass Manager
1580 Dominator Set Construction
1581 Immediate Dominators Construction
1582 Global Common Subexpression Elimination
1583<b>-- Dominator Set Construction</b>
1584-- Immediate Dominators Construction
1585-- Global Common Subexpression Elimination
1586<b> Hello World Pass
1587-- Hello World Pass
1588 Dominator Set Construction</b>
1589 Natural Loop Construction
1590 Loop Invariant Code Motion
1591-- Natural Loop Construction
1592-- Loop Invariant Code Motion
1593 Module Verifier
1594-- Dominator Set Construction
1595-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1596 Bitcode Writer
1597--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1598Hello: __main
1599Hello: puts
1600Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1601</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1602
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1603<p>Here we see that the <a href="#basiccode">Hello World</a> pass has killed the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1604Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1605we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1606href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1607
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1608<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1609 <i>// We don't modify the program, so we preserve all analyses</i>
1610 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1611 AU.setPreservesAll();
1612 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1613</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1614
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1615<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1616
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1617<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1618$ opt -load ../../../Debug+Asserts/lib/Hello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1619Pass Arguments: -gcse -hello -licm
1620Module Pass Manager
1621 Function Pass Manager
1622 Dominator Set Construction
1623 Immediate Dominators Construction
1624 Global Common Subexpression Elimination
1625-- Immediate Dominators Construction
1626-- Global Common Subexpression Elimination
1627 Hello World Pass
1628-- Hello World Pass
1629 Natural Loop Construction
1630 Loop Invariant Code Motion
1631-- Loop Invariant Code Motion
1632-- Natural Loop Construction
1633 Module Verifier
1634-- Dominator Set Construction
1635-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1636 Bitcode Writer
1637--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1638Hello: __main
1639Hello: puts
1640Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1641</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1642
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1643<p>Which shows that we don't accidentally invalidate dominator information
1644anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1645
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1646<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1647<h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1648 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1649</h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1650
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1651<div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1652
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1653<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1654 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1655</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1656
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1657<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1658results, and how long to keep them around for. Because the lifetime of the pass
1659object itself is effectively the entire duration of the compilation process, we
1660need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1661<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1662
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1663<p>If you are writing an analysis or any other pass that retains a significant
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1664amount of state (for use by another pass which "requires" your pass and uses the
1665<a href="#getAnalysis">getAnalysis</a> method) you should implement
Dan Gohmand87c9e32009-06-15 18:22:49 +0000[diff] [blame]1666<tt>releaseMemory</tt> to, well, release the memory allocated to maintain this
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1667internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1668class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1669
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1670</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1671
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1672</div>
1673
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1674<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1675<h2>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1676 <a name="registering">Registering dynamically loaded passes</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1677</h2>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1678<!-- *********************************************************************** -->
1679
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1680<div>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1681
1682<p><i>Size matters</i> when constructing production quality tools using llvm,
1683both for the purposes of distribution, and for regulating the resident code size
1684when running on the target system. Therefore, it becomes desirable to
1685selectively use some passes, while omitting others and maintain the flexibility
1686to change configurations later on. You want to be able to do all this, and,
1687provide feedback to the user. This is where pass registration comes into
1688play.</p>
1689
1690<p>The fundamental mechanisms for pass registration are the
1691<tt>MachinePassRegistry</tt> class and subclasses of
1692<tt>MachinePassRegistryNode</tt>.</p>
1693
1694<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1695<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1696communicates additions and deletions to the command line interface.</p>
1697
1698<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1699information provided about a particular pass. This information includes the
1700command line name, the command help string and the address of the function used
1701to create an instance of the pass. A global static constructor of one of these
1702instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1703the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1704in the tool will be registered at start up. A dynamically loaded pass will
1705register on load and unregister at unload.</p>
1706
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1707<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1708<h3>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1709 <a name="registering_existing">Using existing registries</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1710</h3>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1711
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1712<div>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1713
1714<p>There are predefined registries to track instruction scheduling
1715(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1716machine passes. Here we will describe how to <i>register</i> a register
1717allocator machine pass.</p>
1718
1719<p>Implement your register allocator machine pass. In your register allocator
1720.cpp file add the following include;</p>
1721
1722<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1723 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1724</pre></div>
1725
1726<p>Also in your register allocator .cpp file, define a creator function in the
1727form; </p>
1728
1729<div class="doc_code"><pre>
1730 FunctionPass *createMyRegisterAllocator() {
1731 return new MyRegisterAllocator();
1732 }
1733</pre></div>
1734
1735<p>Note that the signature of this function should match the type of
1736<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1737"installing" declaration, in the form;</p>
1738
1739<div class="doc_code"><pre>
1740 static RegisterRegAlloc myRegAlloc("myregalloc",
1741 " my register allocator help string",
1742 createMyRegisterAllocator);
1743</pre></div>
1744
1745<p>Note the two spaces prior to the help string produces a tidy result on the
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1746-help query.</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1747
1748<div class="doc_code"><pre>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1749$ llc -help
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1750 ...
Duncan Sands18619b22010-02-18 14:37:52 +0000[diff] [blame]1751 -regalloc - Register allocator to use (default=linearscan)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1752 =linearscan - linear scan register allocator
1753 =local - local register allocator
1754 =simple - simple register allocator
1755 =myregalloc - my register allocator help string
1756 ...
1757</pre></div>
1758
1759<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1760an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1761<tt>RegisterScheduler</tt> class. Note that the
1762<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1763<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1764
1765<p>To force the load/linking of your register allocator into the llc/lli tools,
1766add your creator function's global declaration to "Passes.h" and add a "pseudo"
1767call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1768
1769</div>
1770
1771
1772<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1773<h3>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1774 <a name="registering_new">Creating new registries</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1775</h3>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1776
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1777<div>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1778
1779<p>The easiest way to get started is to clone one of the existing registries; we
1780recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1781are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1782
1783<p>Then you need to declare the registry. Example: if your pass registry is
1784<tt>RegisterMyPasses</tt> then define;</p>
1785
1786<div class="doc_code"><pre>
1787MachinePassRegistry RegisterMyPasses::Registry;
1788</pre></div>
1789
1790<p>And finally, declare the command line option for your passes. Example:</p>
1791
1792<div class="doc_code"><pre>
1793 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
Dan Gohman364a39f2008-10-14 17:00:38 +0000[diff] [blame]1794 RegisterPassParser&lt;RegisterMyPasses&gt; &gt;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1795 MyPassOpt("mypass",
1796 cl::init(&amp;createDefaultMyPass),
1797 cl::desc("my pass option help"));
1798</pre></div>
1799
1800<p>Here the command option is "mypass", with createDefaultMyPass as the default
1801creator.</p>
1802
1803</div>
1804
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1805</div>
1806
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1807<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1808<h2>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1809 <a name="debughints">Using GDB with dynamically loaded passes</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1810</h2>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1811<!-- *********************************************************************** -->
1812
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1813<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1814
1815<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1816should be. First of all, you can't set a breakpoint in a shared object that has
1817not been loaded yet, and second of all there are problems with inlined functions
1818in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1819GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1820
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1821<p>For sake of discussion, I'm going to assume that you are debugging a
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1822transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1823on that.</p>
1824
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1825<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1826<h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1827 <a name="breakpoint">Setting a breakpoint in your pass</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1828</h4>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1829
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1830<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1831
1832<p>First thing you do is start <tt>gdb</tt> on the <tt>opt</tt> process:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1833
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1834<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1835$ <b>gdb opt</b>
1836GNU gdb 5.0
1837Copyright 2000 Free Software Foundation, Inc.
1838GDB is free software, covered by the GNU General Public License, and you are
1839welcome to change it and/or distribute copies of it under certain conditions.
1840Type "show copying" to see the conditions.
1841There is absolutely no warranty for GDB. Type "show warranty" for details.
1842This GDB was configured as "sparc-sun-solaris2.6"...
1843(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1844</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1845
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1846<p>Note that <tt>opt</tt> has a lot of debugging information in it, so it takes
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1847time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1848(the shared object isn't loaded until runtime), we must execute the process, and
1849have it stop before it invokes our pass, but after it has loaded the shared
1850object. The most foolproof way of doing this is to set a breakpoint in
1851<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1852want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1853
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1854<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1855(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1856Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1857(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]</b>
1858Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1859Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
186070 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1861(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1862</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1863
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1864<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1865now free to set breakpoints in your pass so that you can trace through execution
1866or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1867
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1868</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1869
1870<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1871<h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1872 <a name="debugmisc">Miscellaneous Problems</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1873</h4>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1874
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1875<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1876
1877<p>Once you have the basics down, there are a couple of problems that GDB has,
1878some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1879
1880<ul>
1881<li>Inline functions have bogus stack information. In general, GDB does a
1882pretty good job getting stack traces and stepping through inline functions.
1883When a pass is dynamically loaded however, it somehow completely loses this
1884capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1885from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1886
1887<li>Restarting the program breaks breakpoints. After following the information
1888above, you have succeeded in getting some breakpoints planted in your pass. Nex
1889thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1890and you start getting errors about breakpoints being unsettable. The only way I
1891have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1892already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1893execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1894
1895</ul>
1896
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1897<p>Hopefully these tips will help with common case debugging situations. If
1898you'd like to contribute some tips of your own, just contact <a
1899href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1900
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1901</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1902
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1903</div>
1904
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1905<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1906<h2>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1907 <a name="future">Future extensions planned</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1908</h2>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1909<!-- *********************************************************************** -->
1910
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1911<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1912
1913<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1914some nifty stuff, there are things we'd like to add in the future. Here is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1915where we are going:</p>
1916
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1917<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1918<h4>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1919 <a name="SMP">Multithreaded LLVM</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1920</h4>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1921
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1922<div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1923
1924<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1925fast enough: obviously we should allow for a multithreaded compiler. Because of
1926the semantics defined for passes above (specifically they cannot maintain state
1927across invocations of their <tt>run*</tt> methods), a nice clean way to
1928implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1929to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1930instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1931
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1932<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1933multithreaded constructs, requiring only the LLVM core to have locking in a few
1934places (for global resources). Although this is a simple extension, we simply
1935haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1936Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1937
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1938</div>
1939
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1940</div>
1941
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1942<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1943<hr>
1944<address>
1945 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]1946 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1947 <a href="http://validator.w3.org/check/referer"><img
Misha Brukmanf00ddb02008-12-11 18:23:24 +0000[diff] [blame]1948 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1949
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1950 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
NAKAMURA Takumib9a33632011-04-09 02:13:37 +0000[diff] [blame]1951 <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1952 Last modified: $Date$
1953</address>
1954
1955</body>
1956</html>